Gas burner control with lagged thermal element to prevent immediate reignition



April 4, 1967 w. H. BRANCHE 3,312,270

GAS BURNER CONTROL WITH LAGGED THERMAL ELEMENT TO PREVENT IMMEDIATE RE-IGNITION Filed April 15, 1965 2 Sheets-Sheet 1 FIG.2

i I I68 x l 1 .5 g 54 Y 3 29 I 2 56 as 1 7s :2 I w i so 1 I I 3: 34 I -|--|3 INVENTOR. WILLIAM H. BRANCHE.

ATTORNEY April 4, 1967 w. H. BRANCHE 3,312,270

GAS BURNER CONTROL WITH LAGGED THERMAL ELEMENT TO PREVENT IMMEDIATE RBI-IGNITION Filed April 15, 1965 2 Sheets-Sheet 2 FIG. 4

INVENTOR.

WILLIAM H. BRANCHE.

ATTORNEY.

United States Patent 3 312 270 -GAS BURNER CONTROL WITH LAGGED THER- MAL ELEMENT TO PREVENT IMMEDIATE RE- IGNITION William H. Branche, Indianapolis, Ind., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Apr. 13, 1965, Ser. No. 447,628 3 Claims. (Cl. 158-124) This invention relates to gas burning apparatus and, more particularly, to gas burning apparatus having means to ignite or automatically re-ignite an extinguished pilot flame.

It is frequently desirable to locate a gas burning apparatus such as a warm air furnace duct heater or unit heater in an attic, rooftop, or other inaccessible location in order to conserve floor space. It will be apparent that with such installations it is often inconvenient to service the gas burning apparatus in the event that the pilot is accidentally extinguished such as by air turbulence or a mometnary drop in gas pressure. It is therefore desirable to provide some means for automatically re-igniting the pilot in the event that the pilot flame is extinguished, without requiring the attention of the user. Furthermore, it is desirable to be able to automatically place the gas burning apparatus in operation after a period of intentional shutdown without having to gain access to the apparatus inorder to manually relight the pilot.

A'problem exists, however, if the gas burning apparatus is provided with an automatic re-ignition system, in the event that the system should attempt to relight the pilot during periods of time when an explosive or combustible gas mixture exists in the combustion chamber of the appar atus. In the event that the automatic re-ignition system attempts to relight the pilot flame while there is a substantial quantity of gas in the combustion chamber, a serious explosion could result. It is therefore desirable to provide a system whereby accidental explosions of the type described are prevented.

Automatic re-ignition systems of the type using an ignition coil for lighting the pilot flame can also damage the ignition coil in the event that the supply of gas to the pilot is accidentally blocked or the draft is too great to permit lighting of the pilot flame. Since the ignition coil is relatively delicate and operates at a rather high surface temperature, in the neighborhood of 2,000 F., continuous operation of the ignition coil under conditions where the pilot flame fails to ignite can cause the ignition coil to burn out in a relatively short period of time. It will be apparent that after the ignition coil has burned out the gas burning apparatus is no longer capable of automatic reignition, and the pilot must be repaired or replaced before the apparatus is put in service again.

Accordingly, it is a principal object of this invention to provide an improved gas burning apparatus having means to automatically light a pilot flame.

It is a further object of this invention to provide a gas burning apparatus having automatic re-ignition means which operates only after an explosive or combustible mixture of gas in the apparatus has been purged therefrom.

It is a still further object of this invention to provide means for automatically relighting the pilot flame on a 3,312,270 Patented Apr. 4, 1967 gas burning apparatus which protects the re-ignition device from burning out in the event of failure of the pilot to ignite.

These and other objects of this invention are achieved in the illustrated preferred embodiment thereof by providing a gas burning apparatus having a gas burner and pilot disposed in a combustion chamber thereof. An electri cally actuated gas valve is provided to supply gas to the burner. A pilot assembly is provided having an ignition coil for lighting a pilot flame, and having a pair of thermally responsive switches for controlling the operation of the apparatus. The first thermally responsive switch is in heat exchange relation with the pilot flame and in its cold position completes a circuit through the ignition device, while in its hot position, it breaks the circuit through the ignition device and establishes a circuit to open the gas valve to the main burner of the apparatus. The second thermally responsive switch is in heat exchange relation with both the pilot flame and the ignition coil. In its cold position, the second switch establishes a circuit through the ignition coil which is broken when the switch become-s hot either due to igniting of the pilot flame or prolonged operation of the ignition coil. In the event the pilot fails to ignite, the heat from the ignition coil Will cause the second thermally responsive switch to open so as to provide a period of time for the ignition coil to cool thus prolonging its life.

The first thermally responsive switch is designed to operate relatively rapidly so as to discontinue the supply of current to the ignition coil soon after the pilot flame is ignited and to discontinue the supply of current to the gas valve of the apparatus soon after the pilot flame is extinguished. The second thermally responsive switch is designed to operate relatively slowly so that several minutes must elapse after the extinguishing of the pilot flame before an attempt is made to automatically relight the pilot. Thus a period of time is automatically provided to purge any remaining explosive mixture of gas in the combustion chamber of the apparatus and one of the serious disadvantages of prior automatically re-ignition systems is avoided.

These and other objects of this invention will become more readily apparent by referring to the following specification and drawings wherein:

FIGURE 1 is a schematic diagram of a gas burning apparatus showing the gas valves arranged in the gas supply lines;

FIGURE 2 is a cross sectional view through a gas pilot assembly made in accordance with this invention;

FIGURE 3 is a perspective view showing the ignition assembly detached from the remainder of the pilot assembly; and

FIGURE 4 is a schematic diagram of the electrical Wiring of an improved gas burning apparatus in accordance with this invention.

Referring particularly to the drawings, there is shown in FIGURE 1 a gas burning apparatus 10 such as a furnace,- unit heater, or duct heater having a main gas burner 11 and a pilot assembly 13 disposed in combustion chamber 12. A suitable flue 14 is provided to discharge waste gas from the combustion chamber and to purge unburned achieved -by the normal or forced draft which withdraws gases from the combustion chamber.

A gas main supplies gas through a manual shutoff valve 16, a gas pressure regulator valve 17, and a solenoid-actuated, electrically controlled main gas valve 18 to main burner 11. A pilot gas line 20 is connected to gas main 15 and supplies gas through a manual shutoif valve 21 and a pilot gas pressure switch 22 to pilot burner assembly 13.

As shown in FIGURE 4, a dropping resistor 26 may be provided to produce the voltage supplied to an ignition coil 28 if desired. Ignition coil 28 comprises a relatively high resistance wire which, when current is passed through it, may obtain a surface temperature of approximately 2,000 F. Ignition coil 28 is disposed in proximity with the gas outlet of pilot 13 so as to ignite the pilot flame. A pilot gas pressure switch 22 is provided with terminals 27 in series with ignition coil 28 to prevent operation of the ignition coil during periods of time when gas pressure is not present in the pilot gas line to prevent the ignition coil from being energized. Alternatively, a spark or other ignition device may be employed in place of ignition coil 28 by suitable circuit modification without departing from the principles of this invention.

Pilot assembly 13 includes a thermostatically actuated, bimetallic, normally closed switch 30 having terminals 29 and 31 which is connected in series with normally closed contacts 34 and 36 of a thermostatically operated switch to complete a current circuit through the ignition coil 28.

Switch 35 is also provided with normally open contact 37 which is closed when the switch is in a hot condition. When pilot assembly 13 has been heated by the pilot flame, switch 35 opens the connection between terminals 36 and 34 and closes the connection between terminals 36 and 37, thus completing a current circuit through the solenoid actuator of gas valve 18, a limit control 38, and a room thermostat 39. Assuming that room thermostat 39 is closed and is therefore calling for heat, and assuming that limit control 38 is closed, indicating no abnormal temperature condition in the apparatus, gas valve 18 will be opened when switch 35 closes the connection between terminals 36 and 37 and a gas will be supplied to the main burner of apparatus 10.

As will be seen in FIGURE 3, pilot assembly 13 preferably comprises a pilot assembly body member 40 and an ignition assembly 41 which may be detachably secured to each other by inserting lugs 42 of the ignition assembly into slots 43 formed in the pilot assembly body. Additionally, securing screw 44 is provided to maintain the parts in assembled engagement with each other.

As best seen in FIGURE 2, pilot assembly is provided with a gas orifice through which gas is supplied from pilot gas line 20. A plurality of apertures 51 are provided to admit primary air into pilot stem 53. The mixture of gas and air is discharged at a target 52 which is preferably tilted as shown in the drawing so that the pilot flame is directed at main gas burner 11 and also impinges on the thermal actuator of switch 35 which will subsequently be described.

As previously explained, switch 30, which is preferably of the bimetallic type, is disposed in heat exchange relation with both the pilot flame and ignition coil 28. Switch 30 is preferably secured to an insulating switch block 54 by means of a suitable rivet 57. A hood 55 extends over switch 30 and ignition coil 28 and is insulated from the switch by a layer of electrical insulation 56. A lead 58 is connected to a preferably adjustable terminal 31 of switch 30. Terminal 29 of switch 30 is connected directly to one terminal of ignition coil 28 and the other terminal of the ignition coil is connected to lead 59 which projects from ignition assembly 41.

Ignition assembly 41 is detachably secured to pilot assembly body member 40. Air holes 63 are formed in body member 40 to supply secondary air to the pilot flame and to cool the actuator of switch 35.

Switch 35 has a thermostatic actuator member 65 having a first leg 66 disposed in heat exchange relation with the pilot flame and a second leg 67. One end of legs 66 and 67 are both rigidly secured to body portion 68 and the other ends are joined by an integral web 69. An insulated tip of adjusting screw 70 engages one end of switch 35 and a second adjustable screw 71 is provided as a pivot point about which the switch blade rotates. An integral, flexible conducting web portion 75, formed by slitting switch blade 35, is connected to terminal 36. Suitable electrical leads 76, 77 and 78 are connected to terminals 36, 34 and 37 respectively.

As shown in the drawing switch 35 is in its normal or cold position. However, when a pilot flame is present, leg 66 of actuator 65 is heated to a greater extent than leg 67 and since the legs are connected to each other at their ends, the differential expansion causes the actuator element to move to the left. The movement of actuator screw 70 to the left causes switch blade 35 to rotate about pivot screw 71 thus closing the connection between contacts 36 and 37 while breaking the connection between contacts 36 and 34.

In operation, it will be apparent that in the event pilot assembly 13 is cold, a circuit through ignition coil 28 is completed upon opening of manual valve 21 which causes gas pressure to closecontacts 27 of pilot gas pressure switch 22. The heat of ignition coil 28 will cause the pilot to ignite. Heat from the pilot flame will cause switch 35, which is in heat exchange relation therewith, to open the connection between contacts 36 and 34 and close the connection between contacts 36 and 37. Opening of the connection with contact 34 causes the supply of current through ignition coil 28 to be discontinued, and closing of the connection with contact 37 will energize main gas valve 18 upon closing of thermostat 39 sensing a heating need so that gas is supplied to main burner 11. Consequently, main burner 11 will be ignited by the pilot flame.

Switch 35 is a relatively rapidly actuated type so that it preferably operates to open the connection with contact 34 and close the connection with contact 37 in approximately a minute after ignition of the pilot flame. The characteristic is achieved by adjusting the thermal storage effect of the pilot assembly body and block 72, which are in heat exchange relation with the pilot flame, to achieve relatively rapid cooling of actutaor 65.

It will be observed that switch 30, which is also in heat exchange relation with the pilot flame and the pilot assembly, will also eventually open to interrupt the connection between terminals 29 and 31 through which current may be supplied to ignition coil 28. Switch 30 is designed so that the thermal storage due to the mass of ignition assembly 41 and block 54, which are heated by the pilot flame, causes the switch to cool relatively slowly and the contact between terminals 29 and 31 is not established until a period of five to ten minutes after the pilot flame becomes extinguished. Thus it will be seen that in the event of accidental or intentional extinguishing of the pilot flame, switch 35 may return to its cold position relatively rapidly to shut off the main gas valve 18 but switch 30 will not complete the circuit through ignition coil 28 for a substantial period of time. During this period of time, which is preferably between five and ten minutes after the pilot flame has been extinguished, the normal or forced draft through combustion chamber 12 Will cause any substantial accumulations of gas in the combustion chamber to be purged through flue 14 so that an explosion will not take place when the pilot assembly attempts to automatically reestablish the pilot flame.

In the event that the pilot flame fails to ignite for any reason, ignition coil 28 will remain energized by the electrical current for approximately a minute before it heats the ignition assembly including switch blade 30 sufflciently to cause contacts 29 and 31 to open. Thereafter bimetal switch 30 will slowly cool and in about another minute will complete a circuit through coil 28 in order to make riod. The cycle time can be adjusted as desired by adjusting screw 31.

It will be appreciated that the life of the ignition coil is greatly increased under these circumstances not only because of the relatively short period of time during which the ignition coil is energized when the pilot flame fails to ignite, but also because the coil is given the opportunity to cool after each period ofoperation. The cycling of the ignition coil described also makes it possible to use a smaller transformer 25 since its tendency to overheat is minimized by the intermittent cycling operation.

It will be appreciated that the invention described herein may be employed to ignite a burner or pilot in response to a thermostatic or other control instead of as an automatic reignition device for constant burning pilots. It

will be appreciated that many ways to embody the foregoing invention may be envisioned within the scope of the following claims, and that there has been described merely a preferred embodiment thereof in order to illustrate its operation.

I claim:

1. A gas burning apparatus having an automatic ignition system operative to automatically ignite a pilot flame comprising:

(a) a gas valve controlling the supply of gas to a burner in a combustion chamber of said apparatus;

(b) pilot means to provide a pilot flame;

(c) a pilot ignition coil disposed in a position to ignite said pilot flame;

(d) a first temperature actuated switch having a cold position in which one circuit is closed and having a warm position in which said one circuit is broken and another circuit is\ closed, said circuits being connected to energize the main gas valve when said switch means is in said warm position thereof and to energize said pilot ignition coil when said first switch is in said cold position thereof, said first switch means being in heat exchange relation with said pilot flame, and said first switch means having a relatively rapid actuation time to deenergize said ignition means in a relatively short period of time after said pilot flame is lighted and to deenergize said gas valve a relatively short time after said pilot flame is extinguished;

(e) a body member having a second temperature actuated switch means mounted thereon in series with said first switch in said one circuit, said second switch being operative to energize said ignition coil when said first and said second switches are in a cold position thereof, said second switch means and said body member both being in heat exchange relation with said pilot flame, and said body member having a sufficiently large thermal storage effect so that said second switch means exhibits a relatively slow cooling rate to provide a substantial period of time between the extinguishing of the pilot flame and the energization of the ignition coil, to thereby permit purging of gas from the combustion chamber before said pilot flame is relighted.

2. A gas burning apparatus having an automatic reignition system comprising:

(a) a gas valve having electric actuating means controlling the supply of gas to a burner disposed in a combustion chamber of said apparatus;

(b) a pilot assembly including,

(1 a body member,

(2) a pilot gas outlet for providing a pilot flame mounted on said body member,

( 3) a first thermostatically actuated switch means mounted on said body member in heat exchange relation with said pilot flame, sald first switch having a hot position completing a circuit and a normal cold position completing another circuit,

(4) electrically energizable ignition means mounted on said body member,

(5) a second thermostatically actuated switch means mounted on body member in heat exchange relation with said .pilot flame and said ignition means, said second switch having a normal cold position completing a circuit and having .a hot position breaking said last-named circuit;

(c) circuit means connecting said ignition means in series with said first switch means and said second switch means to a source of electric current when said switches are both in a cold position;

(d) circuit means connecting the gas valve actuating means through said first switch means in its hot position to a source of electric current to open said gas valve; and

(e) said second'switch means being constructed so as to have a relatively slow rate of cooling with respect to said first switch means, due to the thermal storage of said body member with which said second switch is in heat exchange relation, so that a substantial period of time is provided to purge gas from the combustion chamber of said apparatus before said ignition means is automatically energized after said pilot flame is extinguished.

. 3. A gas burning apparatus having an automatic relgnition system comprising:

(a) a gas valve having electric actuating means controlling the supply of gas to a gas burner in a combustion chamber of said apparatus;

(b) a pilot assembly including,

(1) a pilot assembly body member,-

(2) a pilot gas outlet for providing a pilot flame mounted on said pilot assembly body member,

(3) a first thermostatically actuated switch means mounted on said pilot assembly body member in heat exchange relation therewith, said first switch having a hot position completing a circuit and a normal cold position completing another circurt;

(c) an ignition assembly including,

(1) an ignition assembly body member,

(2) an electrically energizable ignition coil mounted on said ignition assembly body member in heat exchange relation therewith,

(3) a second thermostatically actuated switch means mounted on said ignition assembly body member in heat exchange relation therewith, said second switch having a normal cold position completing a circuit and having a hot position breaking said last-named circuit;

((1) said ignition assembly and said pilot assembly being secured to each other and in heat exchange relation with said pilot flame;

(e) circuit means connecting said ignition coil in series with said first switch means and said second switch means to a source of electric current when said switches are both in a cold position;

(f) circuit means connecting the gas valve actuating means through said first switch means in its hot position to a source of electric current to open said gas valve; and

(g) said second switch means being constructed so as to have a relatively slow rate of cooling with respect to said first switch means due to the thermal storage effect of said ignition assembly body member with which said second switch is in heat exchange relation so that a substantial period of time is provided to purge gas from the combustion chamber of said apparatus before said ignition coil is automatically energized after said pilot flame is extinguished, said second switch having a sufficiently rapid rate of heating so that said ignition coil provides heat to open said second switch after a period of time in the event References Cited by the Examiner UNITED of failure of said pilot to ignite, to prolong the life of 10 FREDERICK KETTERER, Primary Examiner.

said ignition coil. 

1. A GAS BURNING APPARATUS HAVING AN AUTOMATIC IGNITION SYSTEM OPERATIVE TO AUTOMATICALLY IGNITE A PILOT FRAME COMPRISING: (A) A GAS VALVE CONTROLLING THE SUPPLY OF GAS TO A BURNER IN A COMBUSTION CHAMBER OF SAID APPARATUS; (B) PILOT MEANS TO PROVIDE A PILOT FLAME; (C) A PILOT IGNITION COIL DISPOSED IN A POSITION TO IGNITE SAID PILOT FLAME; (D) A FIRST TEMPERATURE ACTUATED SWITCH HAVING A COLD POSITION IN WHICH ONE CIRCUIT IS CLOSED AND HAVING A WARM POSITION IN WHICH SAID ONE CIRCUIT IS BROKEN AND ANOTHER CIRCUIT IS CLOSED, SAID CIRCUITS BEING CONNECTED TO ENERGIZE THE MAIN GAS VALVE WHEN SAID SWITCH MEANS IS IN SAID WARM POSITION THEREOF AND TO ENERGIZE SAID PILOT IGNITION COIL WHEN SAID FIRST SWITCH IS IN SAID COLD POSITION THEREOF, SAID FIRST SWITCH MEANS BEING IN HEAT EXCHANGE RELATION WITH SAID PILOT FLAME, AND SAID FIRST SWITCH MEANS HAVING A RELATIVELY RAPID ACTUATION TIME TO DEENERGIZE SAID IGNITION MEANS IN A RELATIVELY SHORT PERIOD OF TIME AFTER SAID PILOT FLAME IS LIGHTED AND TO DEENERGIZED SAID GAS VALVE A RELATIVELY SHORT TIME AFTER SAID PILOT FLAME IS EXTINGUISHED; (E) A BODY MEMBER HAVING A SECOND TEMPERATURE ACTUATED SWITCH MEANS MOUNTED THEREON IN SERIES WITH SAID FIRST SWITCH IN SAID ONE CIRCUIT, SAID SECOND SWITCH BEING OPERATIVE TO ENERGIZE SAID IGNITION COIL WHEN SAID FIRST AND SAID SECOND SWITCHES ARE IN A COLD POSITION THEREOF, SAID SECOND SWITCH MEANS AND SAID BODY MEMBER BOTH BEING IN HEAT EXCHANGE RELATION WITH SAID PILOT FLAME, AND SAID BODY MEMBER HAVING A SUFFICIENTLY LARGE THERMAL STORAGE EFFECT SO THAT SAID SECOND SWITCH MEANS EXHIBITS A RELATIVELY SLOW COOLING RATE TO PROVIDE A SUBSTANTIAL PERIOD OF TIME BETWEEN THE EXTINGUISHING OF THE PILOT FLAME AND THE ENERGIZATION OF THE IGNITION COIL, TO THEREBY PERMIT PURGING OF GAS FROM THE COMBUSTION CHAMBER BEFORE SAID PILOT FLAME IS RELIGHTED. 